Human IL-13 is a 17-kDa glycoprotein cloned from activated T cells (Zurawski et al. 1994 Immunol Today 15: 19-26), and is produced by activated T cells of the Th2 lineage, although Th0 and Th1 CD4+ T cells, CD8+ T cells, and several non-T cell populations such as mast cells also produce IL-13 (Zurawski et al. 1994 Immunol Today 15: 19-26). The function of IL-13 includes immunoglobulin isotype switching to IgE in human B cells (Punnonen et al. 1993 Proc Natl Acad Sci USA 90: 3730-4) and suppressing inflammatory cytokine production in both human and mouse (de Waal Malefyt et al. 1993 J. Immunol 151: 6370-81; Doherty et al. 1993 J. Immunol 151: 7151-60). IL-13 binds to its cell surface receptors, IL-13Ralpha1 and IL-13Ralpha2. The IL-13Ralpha1 interacts with IL-13 with a low affinity (KD˜10 nM), followed by recruitment of IL-4Ra to form the high affinity (KD˜0.4 nM) signaling heterodimeric receptor complex (Aman et al. 1996 J. Biol Chem 271: 29265-70; Hilton et al. 1996 Proc Natl Acad Sci USA 93: 497-501). The IL-4R/IL-13Ralpha1 complex is expressed on many cell types such as B cells, monocyte/macrophages, dendritic cells, eosinophils, basophils, fibroblasts, endothelial cells, airway epithelial cells, and airway smooth muscle cells (Graber et al. 1998 Eur J. Immunol 28: 4286-98; Murata et al. 1998 Int. Immunol 10: 1103-10; Akaiwa et al. 2001 Cytokine 13: 75-84). Ligation of the IL-13Ralpha1/IL-4R receptor complex results in activation of a variety of signal-transduction pathways including signal transducer and activator of transcription (STAT6) and the insulin receptor substrate-2 (IRS-2) pathways (Wang et al. 1995 Blood 86: 4218-4227; Takeda et al. 1996 J. Immunol 157: 3220-3222). The IL-13Ralpha2 chain alone has a high affinity (KD˜0.25-0.4 nM) for IL-13, and functions as both a decoy receptor negatively regulating IL-13 binding (Donaldson et al. 1998 J. Immunol 161: 2317-24), and a signaling receptor that induces TGF-b synthesis and fibrosis via AP-1 pathway in macrophages and possibly other cell types (Fichtner-Feigl et al. 2006 Nature Med. 12: 99-106).
Several studies conducted in preclinical animal models for asthma indicate that IL-13 plays an important role in asthma. These data include resistance to asthma in the IL-13 knockout mice as well as inhibition of the asthma phenotype with IL-13 antagonists (soluble IL-13 receptors, anti-IL-13 mAbs, etc.) in various mouse models (Sela 1999 Harefuah 137 317-9; Wills-Karp et al. 2003 Curr Opin Pulm Med 9: 21-27; Wills-Karp 2004 Immunol Rev 202: 175-190). Multiple studies have demonstrated that pharmacologic administration of recombinant IL-13 to the lungs of mice as well as guinea pigs induces airway mucus hyper-secretion, eosinophilia and AHR (Grunig et al. 1998 Science 282: 2261-3; Wills-Karp et al. 1998 Science 282: 2258-61; Kibe et al. 2003 Am J Respir Crit Care Med 167: 50-6; Vargaftig et al. 2003 Am J Physiol Lung Cell Mol Physiol 284: L260-9; Vargaftig et al. 2003 Am J Respir Cell Mol Biol 28: 410-9). These effects of IL-13 are reproduced in transgenic mouse systems with either constitutive or inducible expression of IL-13 (Zhu et al. 1999 J Clin Invest 103: 779-788; Zhu et al. 2001 Am J Respir Crit Care Med 164: S67-70; Lanone et al. 2002 J. Clin Invest 110: 463-74). Chronic transgenic over-expression of IL-13 also induces subepithelial fibrosis and emphysema. Mice deficient in the IL-13 (and IL-4) signaling molecule STAT6 fail to develop allergen-induced AHR and mucus overproduction (Kuperman et al. 2002 Nature Med. 8: 885-9). Studies using soluble IL-13 receptor fusion protein (sIL-13Ralpha2Fc) have demonstrated the pivotal role of this cytokine in experimental allergen ovalbumin (OVA)-induced airway disease (Grunig et al. 1998 Science 282: 2261-3; Wills-Karp et al. 1998 Science 282: 2258-61; Taube et al. 2002 J. Immunol 169: 6482-9). Efficacy of anti-IL-13 treatment was also demonstrated in a chronic model of murine asthma. In addition to exhibiting features of mucus hyper-secretion and AHR, this model of chronic asthma demonstrates several hallmarks of human disease that are lacking in the more acute models. These include eosinophilia of the lung tissue located in inter-epithelial spaces as well as smooth muscle fibrosis as measured by increases in collagen deposition. The chronic asthma model is induced with repeated aerosol challenges with OVA in OVA-sensitized mice 1×/week for a total of 4 weeks. Anti-IL-13 antibody administered for the final 2 weeks of OVA challenges (from day 36 with efficacy readouts assessed on day 53 of study) significantly inhibited AHR, pulmonary inflammation, goblet cell hyperplasia, mucus hypersecretion, and airway fibrosis (Yang et al. 2005 J. Pharmacol. Exp. Ther., 313: 8-15). Moreover, therapeutic effect of IL-13 antagonist was also demonstrated to inhibit AHR in a primate model of asthma [Abstract, American Thoracic Society 2005].
IL-13 is implicated in the pathogenesis of human asthma as elevated levels of IL-13 mRNA and protein have been detected in lungs of asthmatic patients, which correlate with severity of the disease (Huang et al. 1995 J. Immunol 155: 2688-94). In addition, human IL-13 genetic polymorphisms, which lead to elevated IL-13 levels, have been identified and are associated with asthma and atopy (Heinzmann et al. 2000 Hum Mol Genet 9: 549-59; Hoerauf et al. 2002 Microbes Infect 4: 37-42; Vercelli 2002 Curr Opin Allergy Clin Immunol 2: 389-93; Heinzmann et al. 2003 J. Allergy Clin Immunol 112: 735-9; Chen et al. 2004 J. Allergy Clin Immunol 114: 553-60; Vladich et al. 2005 J. Clin Invest), and elevated IL-13 levels have been detected in the lung of asthma patients (Huang et al. 1995 J. Immunol 155: 2688-94; Arima et al. 2002 J. Allergy Clin Immunol 109: 980-7; Berry et al. 2004 J. Allergy Clin Immunol 114: 1106-9). A genetic linkage between IL-13 and asthma has also been demonstrated as individuals with a polymorphism in the IL-13 gene which causes higher plasma IL-13 levels have an increased risk for atopy and asthma (Wills-Karp 2000 Respir Res 1: 19-23).
Due to the role of human IL-13 in a variety of human disorders, therapeutic strategies have been designed to inhibit or counteract IL-13 activity. In particular, antibodies that bind to, and neutralize, IL-13 have been sought as a means to inhibit IL-13 activity. However, there exists a need in the art for improved antibodies capable of binding IL-13. Preferably the antibodies bind human IL-13. Preferably the antibodies are capable of neutralizing human IL-13. The present invention provides a novel family of binding proteins, CDR grafted antibodies, humanized antibodies, and fragments thereof, capable binding human IL-13, binding with high affinity, and binding and neutralizing human IL-13.